Mathematical models are to be developed for theoretical prediction of particle deposition and distribution along the respiratory tract system. Specifically, the following tasksare to be undertaken during the period of requested support: 1. Develop a mathematical model for deposition in man at nose-breathing. 2. Recommend figures for the regional deposition in the human lung at nose and mouth-breathing under various working conditions. Emphasis will be given to fine particles which are difficult to be removed from power plant emissions. 3. Develop a mathematical model for depostion in smokers and patients with chronic obstructive pulmonary disease. 4. Develop a mathematical model for deposition in experimental animals. The basic method to be used is the one previously developed by the principal investigator and his faculty associate.